Liquid-absorbent sheet and method for producing the same

ABSTRACT

A liquid-absorbent sheet containing: a liquid-absorbent surface material mainly containing a pulp; a liquid-absorbent nonwoven fabric; a liquid-absorbent rear material mainly containing a pulp; and a super absorbent polymer; wherein the super absorbent polymer is disposed at least between the liquid-absorbent surface material and the liquid-absorbent nonwoven fabric as an A layer and between the liquid-absorbent nonwoven fabric and the liquid-absorbent rear material as a B layer, the super absorbent polymer being contained in a total amount of 200 to 400 g/m 2 , which is allocated in the A layer at 30 to 50% by mass, the liquid-absorbent nonwoven fabric layer at 0 to 40% by mass, and the B layer at 30 to 70% by mass, and the content ratio of the super absorbent polymer in the A layer is less than or equal to the content ratio of the super absorbent polymer in the B layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. 119(a)-(d) to JapanesePatent Application No. 2005-302562, filed Oct. 18, 2005, the entirecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid-absorbent sheet that canrapidly absorb and diffuse a liquid excreted from the human body such asurine or menstrual blood, the sheet having a structure for holding theliquid, and a method for producing the same. In particular, the presentinvention relates to a liquid-absorbent sheet available for paperdiapers, sanitary napkins, or the like, and a method for producing thesame. In more particular terms, the present invention relates to aliquid-absorbent sheet that is thin and has a high absorbent rate withless wet-back so as to effectively absorb and hold a liquid excretedfrom the human body.

2. Description of the Related Art

Various absorbent articles that absorb body fluid such as urine ormenstrual blood have been known. The absorbent articles usually includea liquid-permeable top sheet, a liquid-impermeable back sheet, and anabsorbent body disposed between the top sheet and the back sheet. Suchabsorbent articles are typified by disposable paper diapers and sanitarynapkins and required to have a thin and lightweight shape and to havecapabilities for rapidly absorbing and holding the body fluid such asurine or menstrual blood as much as possible without side leakage. Also,in recent years, such absorbent articles have been made compact, andtherefore more stringently demanded to be thin. Moreover, such absorbentarticles have been demanded to absorb the body fluid quickly with littlereturn of the body fluid to the surface thereof at the skin side, and tobe excellent in quality stability.

Such absorbent articles generally include an absorbent body in which asuper absorbent polymer (hereinafter, abbreviated as SAP) is mixed in apulverized pulp. Although the content of the SAP is generally increasedso as to improve the absorbent rate, such an increase makes theabsorbent body thicker, and thereby it becomes difficult to make theabsorbent article compact. Moreover, although the SAP is usually addedduring pulverizing a sheet pulp to be mixed and pulverized with the pulpso as to reduce unevenness of the quality of obtained absorbent bodies,there is a case in which a part of the SAP is lost during thepulverizing step, and thereby the obtained absorbent bodies do not havesufficient absorbabilities. Moreover, when the thickness of theabsorbent body is reduced by pressurization in addition to the abovestep so as to make the absorbent article thinner, the density of the SAPis increased, which suppresses the permeation of an absorbed liquid, andgaps of the SAP are reduced, which may make the liquid absorbabilityinsufficient.

In order to solve the above problems, Patent Document 1 (Japanese PatentApplication, First Publication No. 2002-35036) has proposed thatperforating holes be formed on the surface of an absorbent body so as toimprove the absorbability thereof. By forming such perforating holes,the absorbed liquid transfers to the back-sheet side at an initialstage, and so the absorbent rate is improved. Moreover, the absorbedliquid spreads around the perforating holes, and so the diffusionproperties are also improved. However, when the perforating holes areformed, the qualities of obtained absorbent bodies vary widely, and awet-back phenomenon in which the absorbed liquid returns through theperforating holes is caused.

On the other hand, Patent Document 2 (Japanese Patent Application, FirstPublication No. H 8-107910) has proposed an absorbent article in whichthe SAP is arranged to form parallel stripes. When the SAP is arrangedto form parallel stripes, the diffusion properties and absorbability ofthe absorbent article are significantly improved, and so the absorbedliquid is rapidly absorbed and diffused. The reason for this is thatvacant spaces produced in such an arrangement enable the SAP absorbingthe liquid to swell. However, since the SAP is unevenly distributed, andso the absorbent article becomes thick, such an arrangement is notsuitable for thinning the article.

Also, Patent Document 3 (Published Japanese translation No. 2003-508647of PCT International Publication) discloses a method for producing anabsorbent material that is used to form an absorbent article, the methodaiming at stabilization of the liquid-absorbability of the absorbentarticle and reduction of the thickness thereof. In the method, the SAPis evenly dispersed in a pulp, and so the stability of the absorbabilityis excellent. Also, a press treatment is carried out so as to preparethe absorbent material as a thin sheet, and so the absorbent material issuitably available for reducing the thickness of the absorbent article.However, since the press treatment is carried out while adding water tothe sheet, the SAP locating at the surface of the sheet is swollen,which may reduce the vacant space, and so the absorbent rate thereof maydecrease.

SUMMARY OF THE INVENTION

The present invention includes the following aspects.

(1) A liquid-absorbent sheet containing: a liquid-absorbent surfacematerial mainly containing a pulp; a liquid-absorbent nonwoven fabric; aliquid-absorbent rear material mainly containing a pulp; and a superabsorbent polymer; in which the super absorbent polymer is disposed atleast between the liquid-absorbent surface material and theliquid-absorbent nonwoven fabric as an A layer and between theliquid-absorbent nonwoven fabric and the liquid-absorbent rear materialas a B layer, the super absorbent polymer being contained in a totalamount of 200 to 400 g/m², which is allocated in A layer at 30 to 50% bymass, the liquid-absorbent nonwoven fabric layer at 0 to 40% by mass,and the B layer at 30 to 70% by mass, and the content ratio of the superabsorbent polymer in the A layer is less than or equal to the contentratio of the super absorbent polymer in the B layer.

(2) A liquid-absorbent sheet according to (1), in which theliquid-absorbent nonwoven fabric is a hydrophilic air laid nonwovenfabric.

(3) A liquid-absorbent sheet according to (1), in which theliquid-absorbent nonwoven fabric contains a pulp and a thermally fusiblesynthetic fiber, and the content ratio of the thermally fusiblesynthetic fiber is 0.1 to 15% by mass with respect to the total mass ofthe nonwoven fabric excluding the super absorbent polymer.

(4) A liquid-absorbent sheet according to (1), in which theliquid-absorbent surface material layer and the A layer, or the B layerand the liquid-absorbent rear material layer are partially intermingled.

(5) A method for producing the liquid-absorbent sheet of (1), including:thermally fusing an interface between the liquid-absorbent surfacematerial layer and the A layer and an interface between theliquid-absorbent rear material layer and the B layer using heating andpressing rollers.

BRIEF DESCRIPTION OF THE DRAWING

Some of the features and advantages of the invention have beendescribed, and others will become apparent from the detailed descriptionwhich follows and from the accompanying drawings, in which:

FIG. 1 is an elevational view indicating an apparatus used forevaluating the liquid absorbability of a liquid-absorbent sheetaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has as its object to solve the above-mentionedproblems. That is, the present invention has as its object to provide aliquid-absorbent sheet which is thin and exhibits a rapid absorbent ratewith less wet-back for the purpose of effectively absorbing and holdingexcreted body fluid, and to provide a method for effectively producingthe liquid-absorbent sheet.

As a result of accumulated investigation carried out so as to solve theabove-mentioned problems, the inventors of the present invention havefound that a thin liquid-absorbent sheet with a rapid absorbent rate andless wet-back can be produced by making it a structure having at leastfive layers, that is, a liquid-absorbent surface material layer mainlycontaining a pulp, a liquid-absorbent nonwoven fabric layer, aliquid-absorbent rear material layer mainly containing a pulp, and atleast two SAP layers containing a SAP, the SPA layers being disposed atleast between the liquid-absorbent surface material layer and theliquid-absorbent nonwoven fabric layer as A layer and between theliquid-absorbent nonwoven fabric layer and the liquid-absorbent rearmaterial layer as B layer, and completed the present invention.

In the following, particular preferred embodiments of theliquid-absorbent sheet according to the present invention will beexplained in more detail. However, this detailed description is notintended to limit the enumerated claims, but to serve as particularexamples thereof.

The liquid-absorbent sheet according to the present invention contains aliquid-absorbent surface material mainly containing a pulp; aliquid-absorbent nonwoven fabric; a liquid-absorbent rear materialmainly containing a pulp; and a super absorbent polymer. Theliquid-absorbent surface material forms a liquid-absorbent surfacematerial layer. The liquid-absorbent nonwoven fabric forms aliquid-absorbent nonwoven fabric layer. The liquid-absorbent rearmaterial forms a liquid-absorbent rear material layer. The superabsorbent polymer forms SAP layers disposed at least between theliquid-absorbent surface material and the liquid-absorbent nonwovenfabric as A layer and between the liquid-absorbent nonwoven fabric andthe liquid-absorbent rear material as B layer.

The liquid-absorbent surface material layer and the liquid-absorbentrear material layer composing the liquid-absorbent sheet according tothe present invention also serve as anti-detaching layers for preventingthe SAP layers (A and B layers) from becoming detached. In order thatthe liquid absorbability of the SAP layers is not suppressed, theliquid-absorbent surface material and the liquid-absorbent rear materialare preferably a hydrophilic base material mainly containing a pulp,such as tissue, absorbent paper, nonwoven fabric, or the like, andexamples thereof include cellulose fiber, such as wood pulp generallyused for manufacturing paper, such as softwood or hardwood chemical pulpor mechanical pulp, recycled pulp, or the like. In addition to thecellulose fiber (pulp), a non-wood pulp such as hemp or cotton, achemosynthetic pulp, a synthetic fiber such as polyester or rayon, orthe like may be included in an amount that does not suppress the liquidabsorbability of the SAP layers. When such a base material is used asthe liquid-absorbent surface material composing the liquid-absorbentsurface material layer, the liquid-absorbent surface material layer ismade to be porous so as to promote liquid permeation. When such a basematerial is used as the liquid-absorbent rear material composing theliquid-absorbent rear material layer, the liquid absorbability andholding properties of the liquid-absorbent sheet become excellent.

The liquid-absorbent nonwoven fabric used for composing theliquid-absorbent nonwoven fabric layer of the liquid-absorbent sheetaccording to the present invention may be made from any materialsprovided that the materials have the liquid permeability and liquidabsorbability, and examples thereof include nonwoven fabric made from afiber such as rayon, polyethylene terephthalate, polypropylene,polyamide, acryl, polyvinyl alcohol, polyethylene, wool, cotton, hemp,pulp, glass, or the like, a blended fiber containing plural kindsthereof, using a suitable processing method such as a spun lace method,a spunbonding method, a thermal bonding method, a chemical bondingmethod, an air laid method, a melt-blown method, a needle punchingmethod, a stitch bond method, or the like.

In the liquid-absorbent nonwoven fabric, a thermally fusible syntheticfiber such as a polyethylene (PE) fiber, a polypropylene (PP) fiber, apolyethylene terephthalate (PET) fiber, a polyamide fiber, a compositefiber of PE and PP, a composite fiber of PE and PET, a composite fiberof PP and PET, a composite of PET and PET, a composite fiber ofpolyamide and polyamide, or the like, is preferably contained so thatthe nonwoven fabric layer and the SAP layers are tightly adhered whenthe layers are heated and pressurized.

As the thermally fusible synthetic fiber, a composite fiber containingPP as a core component and PE as a sheath (shell) component (so-calledcore-sheath or core-shell type composite fiber) or the like ispreferably used.

The thermally fusible synthetic fiber may be contained in such a way asto be deposited with a predetermined thickness on the surface of thenonwoven fabric base material composed of a pulp fiber or the like, orin such a way as to be mixed with the pulp fiber or the like to form anonwoven fabric containing the thermally fusible synthetic fibertogether with the pulp fiber or the like. The thermally fusiblesynthetic fiber may be used in combination of plural kinds thereof, ormay be used in such a way that plural kinds thereof are separatelylaminated. Among these, a hydrophilic air laid nonwoven fabric madeusing the thermally fusible synthetic fiber together with a pulp orother vegetable fibers or the like are preferably used in view of theliquid permeability and the liquid absorbability.

It is preferable that the content of the thermally fusible syntheticfiber in the nonwoven fabric be 0.1 to 15% by mass, and more preferably1 to 15% by mass, with respect to the total mass of the nonwoven fabricexcluding the SAP content so as to prevent deterioration of theabsorbed-liquid holding property and swelling property of the SAP. Whenthe content of the thermally fusible synthetic fiber is less than 0.1%by mass, the thermal fusion may not be able to realize sufficientbonding force for composing the liquid-absorbent sheet. On the otherhand, when the content of the thermally fusible synthetic fiber is morethan 15% by mass, the liquid absorbability of the liquid-absorbentnonwoven fabric layer may become insufficient. As the thermally fusiblesynthetic fiber, one with a fiber length of approximately 3 to 51 mm anda fineness of approximately 1.1 to 7.7 dtex is preferably used.

In the liquid-absorbent nonwoven fabric layer, the SAP is contained inan amount of 0 to 40% by mass with respect to the total mass of the SAPwithout preventing liquid from transferring to B layer laminated on theliquid-absorbent rear material layer.

The SAP used in the present invention can absorb at least 20-fold fluidsuch as urine, body fluid, or the like, with respect to its own weight,and examples thereof include starch-based ones, cellulose-based ones,synthetic polymer-based ones, or the like, such as starch—acrylate graftcopolymers, isobutylene—maleic acid copolymers, saponified starch—ethylacrylate graft copolymers, saponified starch—methyl methacrylate graftcopolymers, saponified starch—acrylonitrile copolymers, saponifiedstarch—acrylamide graft copolymers, acrylate polymers such as sodiumpolyacrylates, polyethylene oxide cross-linked with acrylic acid,cross-linked sodium carboxymethyl celluloses, cross-linked polyvinylalcohol—maleic acid anhydride copolymers, biodegradable polyasparticacid cross-linked by amino acids, SAPs originating from microorganismsthat are cultured products of Alcaligenes Latus, or the like. Amongthese, sodium polyacrylates are preferably used due to the excellentliquid-absorbability thereof. The form of the SAP used in the presentinvention is preferably granular, flake, pellet, short needle, chip, orthe like, so as to be able to be evenly sprayed in a dry state, howeverthe form is not limited to these.

Examples of a method for spraying the SAP include spraying methods usinga slide equipped with a vibrator, screw type feeder, grid roll, or thelike, methods using static electricity such as electrostatic coating, orthe like.

The total content of the SAP contained in the liquid-absorbent sheetaccording to the present invention is 200 to 400 g/m², and preferably200 to 350 g/m². When the total content of the SAP is less than 200g/m², the liquid absorbability of the liquid-absorbent sheet becomesinsufficient. On the other hand, when the total content of the SAP ismore than 400 g/m²; the total mass of the liquid-absorbent sheet becomesextremely large, and so the liquid-absorbent sheet cannot be thinned.

Also, the content ratio of the SAP in A layer disposed between theliquid-absorbent surface material layer and the liquid-absorbentnonwoven fabric layer is 30 to 50% by mass, with respect to the totalmass of the SAP. The content ratio of the SAP in B layer disposedbetween the liquid-absorbent nonwoven fabric layer and theliquid-absorbent rear material layer is 30 to 70% by mass, with respectto the total mass of the SAP. The content ratio of the SAP included inthe liquid-absorbent nonwoven fabric layer is 0 to 40% by mass, withrespect to the total mass of the SAP. The content ratio of the SAP in Alayer is less than or equal to that of the SAP in B layer.

When the content ratio of the SAP in A layer is less than 30% by mass,the amount of wet-back tends to increase. On the other hand, when thecontent ratio of the SAP in A layer is more than 50% by mass, theliquid-absorbent rate tends to decrease.

When the content ratio of the SAP in B layer is less than 30% by mass,although the initial liquid-absorbability is good, the total amount ofthe absorbed liquid tends to decrease. On the other hand, when thecontent ratio of the SAP in B layer is more than 70% by mass, the totalamount of the absorbed liquid tends to decrease and the amount ofwet-back tends to increase.

Moreover, when the content ratio of the SAP in B layer is less than thatof the SAP in A layer, the absorbability of A layer tends to reachsaturation, and so the absorbability of B layer tends not to besufficiently and effectively demonstrated.

When the content ratio of the SAP in the liquid-absorbent nonwovenfabric is more than 40% by mass, the amount of wet-back tends toincrease, and the liquid absorbability tends to become insufficient.

As described above, when the content ratio of the SAP is within theabove-defined range, vacant spaces in A layer are maintained, the liquidpassing through the vacant spaces is instantaneously held in the middlelayer, that is, the liquid-absorbent nonwoven fabric layer, and then theheld liquid smoothly transfers from the middle layer to B layer. Thus,the liquid-absorbent sheet that is thin and exhibits a rapid absorbentrate with less wet-back can be obtained.

The liquid-absorbent sheet according to the present invention can beproduced according to the disclosure of Japanese Patent Application,First Publication No. 2000-135797, for example. In more detail, the SAPis sprayed to deposit on the liquid-absorbent rear material as B layerusing a powder feeder. Then, the above-mentioned materials for theliquid-absorbent nonwoven fabric are mixed and laminated on B layerusing a mat former or the like. Then, the SAP is sprayed on theliquid-absorbent nonwoven fabric to form A layer, and theliquid-absorbent surface material is laminated on A layer. Then, thelaminated body is heated and pressurized so as to produce theliquid-absorbent sheet.

The interface between the liquid-absorbent surface material layer and Alayer and the interface between B layer and the liquid-absorbent rearmaterial layer are thermally fused using heating and pressing rollers.At this time, the SAP is plasticized with the moisture contained thereinand serves as a binder. When the thermally fusible synthetic fiber iscontained in the liquid-absorbent nonwoven fabric layer, theliquid-absorbent surface material and the liquid-absorbent rear materialare adhered more tightly. This is done by using the rollers to heat andpressurize both of the liquid-absorbent surface material layer and theliquid-absorbent rear material layer at the temperature not lower thanthe temperature at which the surface of the thermally fusible syntheticfiber melts. Furthermore, this adherence is achieved due to the effectof tangled molecules of plasticized thermally fusible synthetic fiberand the SAP plasticized with the moisture contained therein. In orderthat the adhesive strength between the liquid-absorbent surface materialand the liquid-absorbent rear material be enhanced, a small amount ofthe moisture is preferably supplied to the liquid-absorbent surfacematerial and the liquid-absorbent rear material. Alternatively,thermally fusible powders or spray adhesives may be applied so as toincrease the adhesive strength. Since the thermal fusing step using theheating and pressing rollers welds the SAP layers and theliquid-absorbent nonwoven fabric again, it is possible to adjust thethickness of the liquid-absorbent sheet at the same time.

In order to further improve the liquid diffusion properties, thehigh-density portion and the low-density portion may be alternatelyarranged on the liquid-absorbent sheet by treating sheet using theheating and pressing emboss rollers with longitudinal stripes or meshesengraved on one or both rollers.

In order to enhance the adhesive strength between the liquid-absorbentsurface material layer and A layer or between the liquid-absorbent rearmaterial layer and B layer, and also to prevent the SAP from unevenlydistributing during preparation, the SAP is preferably made to beintermingled with the liquid-absorbent surface material layer or theliquid-absorbent rear material layer in at least a partial area of theinterface between A layer and the liquid-absorbent surface materiallayer or the interface between B layer and the liquid-absorbent rearmaterial layer.

The liquid-absorbent sheet according to the present invention may beused as an absorbent body in an absorbent article composed of aliquid-permeable top sheet, an absorbent body, and a liquid-impermeableback sheet, or an absorbent body in an absorbent article composed of aliquid-permeable top sheet, a sublayer, an absorbent body, and aliquid-impermeable back sheet. Also, the liquid-absorbent sheetaccording to the present invention may be used as an absorbent body inan absorbent article composed of a sublayer, a liquid-permeable topsheet, an absorbent body, and a liquid-impermeable back sheet.

In this usage, the liquid-absorbent sheet according to the presentinvention is used by placing the liquid-absorbent surface material layeron the top sheet side.

The liquid-absorbent sheet according to the present invention may beused for disposable diapers, sanitary napkins, breast milk pads,water-absorbent sheets, oil-absorbent sheets, pads aiming at absorbing aliquid with a viscosity such as an ink jet printer ink effluent, variouswipes, or the like.

EXAMPLES

In the following, although the present invention will be morespecifically explained by way of examples, it is apparent that thepresent invention is not limited to these. Also, “parts” and “%” used inthe examples indicate “parts by mass” and “% by mass” unless otherwiseso indicated.

Example 1

On a wire, a tissue having a basis weight of 14 m² (manufactured byNippon Tokushu Fabric Co., Ltd.) was unwinded as a liquid-absorbent rearmaterial, and 125 g/m² of a SAP (super absorbent polymer manufactured bySUMITOMO SEIKA CHEMICALS CO., LTD., under the trademark of AQUA KEEP SA60 SX) was sprayed onto the rear material tissue using a powder feeder,and thus B layer was formed on the rear material tissue layer. Onto Blayer, an air laid nonwoven fabric composed of 205 g/m² of a pulp fiberwith a fiber length of 0.05 to 5 mm (softwood bleached kraft pulp (NBKP)manufactured by Oji Paper Co., Ltd.) and 17 g/m² (content ratio: 7.7% bymass) of a PE/PP (core/sheath) fiber with a fineness of 1.7 dtex and alength of 5 mm (manufactured by CHISSO CORPORATION under the trade nameof ESC) was laminated using a mat former, and thus the air laid nonwovenfabric layer was formed on B layer. Then, 125 g/m² of the SAP wassprayed onto the air laid nonwoven fabric layer using a powder feeder,and thus A layer was formed on the air laid nonwoven fabric layer. Then,a tissue with a basis weight of 14 g/m² (manufactured by Nippon TokushuFabric Co., Ltd.) was laminated on A layer as a liquid-absorbent surfacematerial layer, and then the resultant was passed through a drier toobtain an absorbent sheet composed of five layers, that is, the surfacematerial layer, A layer, the air laid nonwoven fabric layer, B layer,and the rear material layer. Both surfaces of this absorbent sheet weretreated using heating and pressing rollers so that the surface materiallayer and the rear material layer were adhered to be fixed. Thus, aliquid-absorbent sheet with a basis weight of 500 g/m² and a thicknessof 2.8 mm was obtained.

Example 2

A liquid-absorbent sheet with a basis weight of 500 g/m² and a thicknessof 2.4 mm was produced in a similar manner to that of Example 1 exceptthat an absorbent sheet composed of five layers, that is, a surfacematerial layer, A layer, an air laid nonwoven fabric layer, B layer, anda rear material layer was prepared as described below. On a wire, thetissue having a basis weight of 14 g/m² was unwound as the rear materiallayer, and 85 g/m² of the SAP was sprayed onto the rear material layerusing a powder feeder, and thus B layer was formed on the rear materiallayer. Onto B layer, an air laid nonwoven fabric composed of 205 g/m² ofthe pulp fiber with a fiber length of 0.05 to 5 mm (NBKP manufactured byOji Paper Co., Ltd.), 17 g/m² (content ratio: 7.7% by mass) of the PE/PP(core/sheath) fiber with a fineness of 1.7 dtex and a length of 5 mm,and 85 g/m² of the SAP was laminated using a mat former, and thus theair laid nonwoven fabric layer was formed on B layer. Then, 80 g/m² ofthe SAP was sprayed onto the air laid nonwoven fabric layer using apowder feeder, and thus A layer was formed on the air laid nonwovenfabric layer. Then, the tissue with a basis weight of 14 g/m waslaminated on A layer as the surface material layer. Then, the resultantwas passed through a drier to obtain the absorbent sheet.

Example 3

A liquid-absorbent sheet with a basis weight of 500 g/m² and a thicknessof 2.9 mm was obtained in a similar manner to that of Example 1 exceptthat an absorbent sheet composed of five layers, that is, a surfacematerial layer, A layer, an air laid nonwoven fabric layer, B layer, anda rear material layer was prepared as described below. On a wire, thetissue having a basis weight of 14 g/m² was unwinded as the rearmaterial layer, and 125 g/m² of the SAP was sprayed onto the rearmaterial layer using a powder feeder, and thus B layer was formed on therear material layer. Onto B layer, an air laid nonwoven fabric composedof 205 g/m² of the pulp fiber with a fiber length of 0.05 to 5 mm (NBKPmanufactured by Oji Paper Co., Ltd.), 17 g/m² (content ratio: 7.7% bymass) of the PE/PP (core/sheath) fiber with a fineness of 1.7 dtex and alength of 5 mm, and 50 g/m² of the SAP was laminated using a mat former,and thus the air laid nonwoven fabric layer was formed on B layer. Then,75 g/m² of the SAP was sprayed onto the air laid nonwoven fabric layerusing a powder feeder, and thus A layer was formed on the air laidnonwoven fabric layer. Then, the tissue with a basis weight of 14 g/m²was laminated on A layer as the surface material layer. Then, theresultant was passed through a drier to obtain the absorbent sheet.

Example 4

A liquid-absorbent sheet with a basis weight of 526 g/m² and a thicknessof 2.7 mm was obtained in a similar manner to that of Example 1 exceptthat an air laid nonwoven fabric mainly containing a pulp with a basisweight of 40 g/m² (KINOCLOTH manufactured by OJI KINOCLOTH Co., LTD.)was used instead of the tissue as the surface material.

Example 5

A liquid-absorbent sheet with a basis weight of 500 g/m² and a thicknessof 2.4 mm was obtained in a similar manner to that of Example 2 exceptthat the surface material layer-side surface of the absorbent sheet wastreated using heating and pressing rollers, one of which has stripeswith intervals of 2 mm, the stripes being engraved in a longitudinaldirection with respect to the width direction of the roller, so that thesurface material layer-side surface has dents and salients with verticaldifferences of 0.4 mm and the thickness of the surface material layer atthe dent is 2.0 mm.

Comparative Example 1

On a wire, the tissue having a basis weight of 14 g/m² was unwinded as arear material layer, onto which an air laid nonwoven fabric composed of189 g/m² of the pulp fiber with a fiber length of 0.05 to 5 mm (NBKPmanufactured by Oji Paper Co., Ltd.) and 33 g/m² (content ratio: 15% bymass) of the PE/PP (core/sheath) fiber with a fineness of 1.7 dtex and alength of 5 mm was laminated using a mat former. Then, 250 g/m² of theSAP was sprayed onto the air laid nonwoven fabric layer using a powderfeeder. Then, the tissue with a basis weight of 14 g/m² was laminated onthe SAP layer as a surface material layer, and then the resultant waspassed through a drier to obtain an absorbent sheet composed of thesurface material, the SAP layer, the air laid nonwoven fabric layer, andthe rear material layer. Both surfaces of this absorbent sheet werefurther treated using heating and pressing rollers to be adhered andfixed. Thus, a liquid-absorbent sheet with a basis weight of 500 g/m²and a thickness of 2.0 mm was obtained.

Comparative Example 2

On a wire, the tissue having a basis weight of 14 g/m² was unwinded as arear material layer, onto which an air laid nonwoven fabric composed of205 g/m² of the pulp fiber with a fiber length of 0.05 to 5 mm (NBKPmanufactured by Oji Paper Co., Ltd.), 17 g/m² (content ratio: 7.7% bymass) of the PE/PP (core/sheath) fiber with a fineness of 1.7 dtex and alength of 5 mm was laminated using a mat former. Then, 125 g/m² of theSAP was sprayed onto the air laid nonwoven fabric layer using a powderfeeder. Then, the tissue with a basis weight of 14 g/m² was laminated onthe SAP layer as the surface material layer, and then the resultant waspassed through a drier to obtain an absorbent sheet composed of thesurface material, the SAP layer, the air laid nonwoven fabric layer, andthe rear material layer. Both surfaces of this absorbent sheet werefurther treated using heating and pressing rollers to be adhered andfixed. Thus, a liquid-absorbent sheet with a basis weight of 500 g/m²and a thickness of 2.8 mm was obtained.

Comparative Example 3

A liquid-absorbent sheet with a basis weight of 430 g/m² and a thicknessof 2.8 mm was obtained in a similar manner to that of Example 1 exceptthat the amount of the SAP sprayed onto the rear material layer was 90g/m² and the amount of the SAP sprayed onto the air laid nonwoven fabriclayer was 90 g/m².

Comparative Example 4

A liquid-absorbent sheet with a basis weight of 500 g/m² and a thicknessof 2.4 mm was obtained in a similar manner to that of Example 2 exceptthat the amount of the SAP sprayed onto the rear material layer was 50g/m², the amount of the SAP contained in the air laid nonwoven fabriclayer was 150 g/m², and the amount of the SAP sprayed onto the air laidnonwoven fabric layer was 50 g/m².

Comparative Example 5

A liquid-absorbent sheet with a basis weight of 500 g/m² and a thicknessof 2.8 mm was obtained in a similar manner to that of Example 1 exceptthat the amount of the SAP sprayed onto the rear material layer was 200g/m² and the amount of the SAP sprayed onto the air laid nonwoven fabriclayer was 50 g/m².

The liquid-absorbent sheets obtained as described above were evaluatedin accordance with the following methods, and results thereof are shownin Table 1.

Preparation of Samples to be Evaluated

Each liquid-absorbent sheet obtained above was cut into a sheet-shapedpiece with a width of 100 mm and a length of 250 mm. On the surfacematerial layer-side surface of the piece, a perforated sheet with abasis weight of 27 g/m² was laminated as a top sheet. On the rearmaterial layer-side surface of the piece, a back sheet with a basisweight of 20 g/m² was laminated. Thus, an absorbent article was obtainedas each sample and evaluated in accordance with the following.

Preparation of Test Solution

0.9% by mass of physiological saline in which 9 g of sodium chloride wasdissolved in 991 g of distilled water was colored with a coloring agent(blue food color No. 1 manufactured by Benifuji Chemical Industry Co.,Ltd.) so as to visually observe effects of the samples, and used as atest solution.

Test with Respect to Absorbent Rate

A special apparatus 4 shown in FIG. 1 was used for measuring theabsorbent rate of each samples. The apparatus 4 was composed of a metalplate (weight) 1 and an acrylic tube 3. The metal plate 1 had a width of80 mm, a length of 80 mm, a thickness of 10 mm, and a weight of 397.7 g.In the center portion of the metal plate 1, a hole 2 with a diameter of41 mm was formed. The acrylic tube 3 had a diameter of 30 mm, a heightof 130 mm, and a weight of 89.2 g. In order to use the apparatus 4, themetal plate 3 was placed on the surface of the sample (not shown in FIG.1), and then the acrylic tube 3 was placed in the hole 2 of the plate 3to make contact with the sample. Then, 80 cc of the test solution wasapplied onto the sample through the acrylic tube and the time requiredfor the test solution to be completely absorbed in the sample wasmeasured. Each sample was tested three times with intervals of 30minutes and measured with respect to the absorbent rate of each time.

Test with Respect to Liquid Diffusion Properties

After every measurement of the absorbent rate as described above, theapparatus 4 was removed from the sample, the longitudinal diffusionlength of the test solution spread on the sample was measured, and theoccurrence of side leakage was checked. Since these steps were conductedafter every measurement of the absorbent rate, these steps wereconducted three times per sample with intervals of 30 minutes.

Wet-Back

When the test solution was completely diffused, that is, 10 minutesafter every measurement of the absorbent rate, a filter paper (No. 2)was placed onto the entire surface of the sample, and then a 3.5-kgweight was placed on the filter paper so that the load was evenlyapplied thereon. 30 seconds after placing the weight, the mass of thetest solution absorbed in the filter paper was measured.

Total Evaluation

Each sample was comprehensively evaluated from the standpoint of usageas a liquid-absorbent sheet.

-   -   A: Very excellent as a liquid-absorbent sheet.    -   B: Excellent as a liquid-absorbent sheet.    -   C: There was a slight problem under a level having no trouble in        practical use as a liquid-absorbent sheet.    -   D: There were problems under a level unpractical as a        liquid-absorbent sheet.    -   E: Very inferior as a liquid-absorbent sheet.

TABLE 1 Diffusion length Absorbent rate (mm) Wet-back Basis (seconds)first/second/third (g) weight Thickness first/second/third Occurrence offirst/second/third Total (g/m²) (mm) Evaluation side leakage Evaluationevaluation Example 1 500 2.8 106/102/120 139/185/250 0.15/1.15/5.49 B BB B Example 2 500 2.4 75/64/64 168/250/250 0.19/2.65/8.89 B B B BExample 3 500 2.9 101/104/114 133/216/250 0.34/2.68/8.66 B B B B Example4 526 2.7 75/58/75 155/203/250 0.06/0.59/5.21 A B B B Example 5 500 2.4111/137/150 250/250/250 0.27/2.45/7.35 B B B B Comparative 500 2.0131/163/211 158/250/250 0.39/6.69/28.0 E Example 1 D D D Comparative 5002.8  93/125/178 180/250/250 0.15/2.13/24.5 D Example 2 C B D Comparative430 2.8 100/128/161 137/175/250 0.15/2.30/17.4 D Example 3 C D DComparative 500 2.4  85/92/172 145/250/250 0.20/2.20/26.5 D Example 4 CD D Comparative 500 2.8  63/110/181 128/225/250 0.23/7.23/18.4 D Example5 C D D

As shown in Table 1, the liquid-absorbent sheets prepared in Examples 1to 5 were thin, rapidly absorbed liquid, and exhibited less wet-back andside leakage. On the other hand, the liquid-absorbent sheets prepared inComparative Examples 1 to 5 were particularly inferior in terms of theliquid-absorbability and wet-back preventability.

As described above, the liquid-absorbent sheet according to the presentinvention has a thin thickness, a rapid absorbent rate, and a highwet-back preventability, and so can effectively absorb and hold thefluid excreted from the human body as compared with conventionalabsorbent sheets. Since the liquid-absorbent sheet according to thepresent invention is compact and excellent in the liquid absorbability,it can be preferably used as a liquid-absorbent sheet composing anabsorbent article such as a paper diaper, sanitary napkin, or the like.

1. A liquid-absorbent sheet comprising: a liquid-absorbent surfacematerial comprising a pulp; a liquid-absorbent nonwoven fabric; aliquid-absorbent rear material comprising a pulp; a super absorbentpolymer; an A layer which is disposed between the liquid-absorbentsurface material and the liquid-absorbent nonwoven fabric; and a B layerwhich is disposed between the liquid-absorbent nonwoven fabric and theliquid-absorbent rear material, wherein the total amount of the superabsorbent polymer is 200 to 400 g/m², which is allocated in the A layerat 30 to 50% by mass, the liquid-absorbent nonwoven fabric layer at 0 to40% by mass, and the B layer at 30 to 70% by mass; and wherein thecontent ratio of the super absorbent polymer in the A layer is less thanor equal to the content ratio of the super absorbent polymer in the Blayer.
 2. A liquid-absorbent sheet according to claim 1, wherein theliquid-absorbent nonwoven fabric is a hydrophilic air laid nonwovenfabric.
 3. A liquid-absorbent sheet according to claim 1, wherein theliquid-absorbent nonwoven fabric comprises a pulp and a thermallyfusible synthetic fiber, and the content ratio of the thermally fusiblesynthetic fiber is 0.1 to 15% by mass with respect to the total mass ofthe nonwoven fabric excluding the super absorbent polymer.
 4. Aliquid-absorbent sheet according to claim 1, wherein theliquid-absorbent surface material layer and the A layer, or the B layerand the liquid-absorbent rear material layer are partially intermingled.5. A method for producing the liquid-absorbent sheet of claim 1,comprising: thermally fusing an interface between the liquid-absorbentsurface material layer and the A layer and an interface between theliquid-absorbent rear material layer and the B layer using heating andpressing rollers.